Electronic components such as semiconductor chips are becoming progressively smaller with each new product release, while at the same time the heat dissipation requirements of semiconductor chips are increasing due to their improved capacity to process more data faster. Commonly, a thermal interface material is utilized between an electronic component and a heat sink in order to efficiently dissipate heat generated by the electronic component.
A conventional thermal interface material is made by diffusing particles with a high heat conduction coefficient in a base material. The particles can be made of graphite, boron nitride, silicon oxide, alumina, silver, or other metals. However, a heat conduction coefficient of the thermal interface material is now considered to be too low for many contemporary applications, because it cannot adequately meet the heat dissipation requirements of modern electronic components.
An article entitled “Unusually High Thermal Conductivity of Carbon Nanotubes” and authored by Savas Berber (page 4613, Vol. 84, Physical Review Letters 2000) discloses that a heat conduction coefficient of a carbon nanotube can be 6600 W/m·K (watts/meter·Kelvin) at room temperature. However, if carbon nanotubes are filled in a base material randomly, each of heat conduction paths within the base material may include two or more adjoining carbon nanotubes. The junction between each two adjoining carbon nanotubes represents a point of thermal resistance when heat travels from one of the carbon nanotubes to the other carbon nanotube. If a heat conduction path contains more than one point of thermal resistance, the sum total of thermal resistance for the heat conduction path may be significant. Further, if the base material contains a large proportion of heat conduction paths having points of thermal resistance, the overall thermal resistance of the filled base material may be unacceptably high.
Because of the above-described problems, a method for producing an aligned carbon nanotube thermal interface structure has been developed. In a batch process, a capacitor is immersed in a bath containing a slurry of thermoplastic polymer containing randomly oriented carbon nanotubes, and is then energized to create an electrical field to orient the carbon nanotubes prior to curing. However, the method necessarily involves rearranging the randomly oriented carbon nanotubes by application of the electrical field. Variations in the electrical field intensity and direction are liable to occur, and this can lead to asymmetric distributions of the carbon nanotubes in the thermal interface structure. When this happens, the overall thermal resistance of the thermal interface structure is increased.
What is needed, therefore, is a method for manufacturing a thermal interface material which ensures that carbon nanotubes in the thermal interface material have good alignment.